The ability to accurately determine one's location has long been a sought after goal. To that end, location determining systems have been developed. For example, GPS and other systems can be used to determine location.
One drawback associated with GPS is that, in some locations, reception of the required satellite signals is poor. Furthermore, GPS requires relatively expensive satellites and precision timing (usually with atomic clocks).
Other drawbacks of GPS systems are that they can experience geometric dilution of precision (GDOP). For example, GDOP can arise from errors propagated through the satellite signal transmission and through round-off errors in calculation.
In addition, the process of searching for and acquiring GPS signals, reading the ephemeris data for a multiplicity of satellites and computing the location of the receiver from this data can be time consuming, often requiring several minutes. In many cases, this lengthy processing time may render the information unusable.
On the other hand, in existing cellular systems a mobile telephone's location within the cellular system can be estimated by measuring a the time difference of arrival (TDOA) of signals transmitted to or from the mobile unit. TDOA depends on a number of factors some of which include, the number of receiving locations, the number of diverse antennas at each cell site, the average distance from the transmitting unit to each of the receiving base stations, the average height of the receiving antennas, and the average antenna power gain in the direction of the transmitting unit. Some TDOA systems may require a large number of well-placed sensors in order to get a robust, enhanced accuracy measurement. Hence, there is a need for fast, relatively inexpensive, yet accurate method of determining the location of an object.
Another drawback of existing systems is that it is that the location of communication transceivers is not always accurately known. Some existing multilateration techniques rely on computations for which the known positions of transceivers is critical. Other drawbacks also exist.